The sparganum of the cestode, Spirometra mansonoides, elaborates a factor similar to pituitary growth hormone, which causes increased growth in various rodents. This effect is limited to the single species mentioned. S. "mansoni" from Asia, Africa, S. America, Australia, does not produce the factor. It was formerly thought that S. m'oides was limited to the eastern U.S. I have recently received material of a morphologically similar form from Brazil and Ecuador. I plan to test this form to determine whether it is physiologically as well as morphologicaly identical with S. m'oides of N. America. We have observed apparent type-C virus particles in the excretory ducts of Spirometra spp. The significance of these is being studied. I am providing generous amounts of material to several collaborative projects: to Dr. Maurice S. Raben, of Boston, who is investigating the physiological properties of the growth factor; to Dr. Monroe S. Glitzer of Merck and Co., who is attempting to determine its structure; to Paul Weinstein of Notre Dame, who is investigating the role of vitamin B12 in the metabolism of the worm; to John Finerty of NIH, who is interested in the effect of the worm in potentiating the immune response of the host. I am providing large quantities of material to our own laboratory, where Holz and his associates are making a detailed study of lipids in all stages of the worm from egg to adult.